Exhaust purification catalyst deterioration diagnosis method and deterioration diagnosis apparatus

摘要

A method of diagnosing deterioration of an exhaust emission control catalyst is provided. The catalyst includes an HC (hydrocarbon) adsorbing part and an oxidation catalyst part. The method includes estimating that an HC discharge amount discharged from the HC adsorbing part is larger than a first value, detecting a parameter relating to a reaction heat of the exhaust emission control catalyst, and diagnosing that the exhaust emission control catalyst is deteriorated when the detected parameter indicates a temperature value lower than a predetermined threshold. The deterioration diagnosis is performed under a first condition that the HC discharge amount is estimated to be larger than the first value.